Process of reducing aluminium by electrolysis



(specimens.)

' C. HALL.;

PROGSSOF REDUGIN UMINIUM BY ELEGTROLYSIS.

No. 400,766. l Patented Apr. 2, 1889.

[IIIIHHJUIIII [72 venan.' Mme-ms.-

MF/Ww UNITED STATES PATENT OFFICE.

CHARLES 'M HALL,

-OF OBERLIN, OHIO.

PROCESS OF REDUCING ALUMINIUM BY ELECTROLYSIS.

SPECIFICATION forming part of Letters Patent N0. 400,766, April 2, 1889.

Application filed July 9, 1886. Serial No. 207,601. (Specimens.)

To all whom it may concern.:

Be it known that I, CHARLES M. IIALL, a

citizen of' the United States, residing at Obert lin,in the county of Lorain and Sta-teef Ohio, E

have invented certain new and useful Improvements 1n the Process of Reducing Aluminium by Electrolysis; and I do hereby de- A clare the following to be a full, clear, and exact. l

description of the invent-ion, such as will enable others skilled in the art to which it apperl tains to make and use the same.

The invention described herein relates to the reduction of aluminium from its oxide i by dissolving such oxide in a bath containing salt of aluminium, substantially as herein- In the accompanying drawings, forming a part of this specification, Figure l is a sectional elevation of a form of apparatus :tp-'

plicable in the practice of my invention; and Fig. 2 is a view, partly in elevation and partly in section,of a modified form of apparatus.

In. the practice of my invention I prepare a bath for the solution of the alumina by fusing together in a suitable Crucible, A, the fluorideof aluminium and the fluoride of a metal more electro-positive than aluminiumas, for example, t-he fluoride of sodium potasslum, dre-these salts being preferably mingled together in the proportions of eightyfour parts of sodium fluoride and one hundred and sixty-nine parts of aluminium fluoride, represent-ed by the formula vNazAlgFs.

A convenient method of forming the bath consists in adding to the mineral cryolite 2.3!;- of itsy weight of aluminium fluoride. The object of thus adding aluminium fluoride is vto secure in the bath the proper relative pro- I mersed in the solution. By the action of the To this fused bath is added alumina or l electric current, which preferably has an eleci tro-motive force ot about four to six volts, oxygen is released at the positive electrode C,

electrode I), which, oir account of the aflinity I of aluminium for other metals, is formed of carbon when it is desired to produce pure aluminium. The positive electrode may be formed of carbon, copper, platinum, or other suitable material. 'hcn formed of carbon, E the electrode C is gradually consumed, and must therefore be renewed from time to time; but when formed of copper an oxide coating is formed over the surface of the electrode. This coating serves toprotect the elect-rode `from further destruction by theaction of the the conduct-ing qualities of the electrode.

materia-ls,f I prefer to form the crucible or melting-pot 'A of metal-as iron or steel-and protect the same from the action of the aluminium by a carbon lining, A. This crucible is placed in a suitable furnace, B, and subjected to a suicient heat. to fuse the materials placed therein, such materials fusing at approximately the same temperature as common salt.

In lien of the electrode' I), as shown in Fig. 1,. the carbon lining A may be employed as the negative electrode, as shown in Fig. 3,the conductor from the negativeI pole of the elec tric generator being suitably connected, as shown at N', to such lining.

In order to render the/.bath or solvent more fusible fluoride of lithium may be substituted for a portion of the fluoride of sodium--as, for example, for one-fourth of the fluoride of vsodium an`e'quivalent amount of lithium fluoride by molecular weights may be substituted. Thus twenty-six parts of lithium fluoride displacing forty-two parts of sodium fluoride, the resulting combina-tion contains tweni ty-six part-s of lithium fluoride for every ,one l hundred and twenty-six parts of sodium fluoride and three hundred and thirty-eight parts of aluminium fluoride.

While I consider the proportions of fluorides of sodium and aluminium, and of the fluorides of sodium, lithium, and aluminium,

and aluminium is reduced at the negative oxygen, but does not interfere materially with,

O11 account of the affinity ot' aluminium for other metals, and also the corrosive actionof the materials forming the bath on cart-hy suitable means; or the bath may be poured out and after being cooled the aluminium may be picked out.

`15 As hereinbefore stated, the oxygen is released at the positive electrode, and when the latter is formed of carbon combines therewith, forming carbonic oxide, (00,) the carbon being gradually consumed, and with some zo salts, more particularly the salts of sodium, carbonaceous material is preferably used in the positive electrode or anode; but when the posit-ive. electrode is formed of copper,'as is,

preferable when salts of potassium are em- 13 ployed, a copper-oxide coating is first formed on the electrode, thereby forminga protective covering, free oxygen being subsequently given oi atthe positive electrode.`

No claim is made herein speciiically to the use of the fluoride of potassium and aluminiumas a' bath forthe reduction of aluminium,

as the same forms the subject-matter of an application filed .February 2 1887, and num# bered Serially 226,206; nor does the apparatus 35 described herein with more or less particularity form any part of the invention herein, as the same forms the subjecbmatter of an' application, No. 282,952, iiled August 17, 1888.

lI claim herein as my invention 1.. As an improvement in the art of manufacturing aluminium, the herein -described process, which consists in dissolving alumina in a fused bath composed of the iluorides of aluminium and a Ametal more electropositive than aluminium, and then passing an electric current through the fused mass, substantially as set forth.

2. As an improvement in the art of manufacturing aluminium, the herein-described process, which consists in dissolving alumina in a fused bath composed of the fluorides of aluminium and sodium, and then passing an electric current, by means of a carbonaceous anode, through the fused mass, substantially as set forth.

,3. As an improvement in the art of manufacturing aluminium, the herein-described process, which consists in dissolving alumina in a fused' bath composed of the iluorides of aluminium, sodium, and lithium, and' then 6o passing an elect-ric current, by means of a carbonaceous anode, through the fused mass, sub stantially as set forth.

In testimony whereof I affix my signature in presence of two witnesses. Y

CHARLES M'. HALL.

Witnesses:

GEORGE E. HALL, Ron'r.' L.FENwicx. 

